Congestive heart failure (CHF), also called congestive cardiac failure (CCF) or just heart failure, is the pathophysiologic state in which the heart, via an abnormality of cardiac function, fails to pump blood at a rate commensurate with the requirements of the metabolizing tissues. Heart failure may be caused by cardiomyopathy, heart valves damage, coronary heart disease, hypertension or in some cases diabetes. The heart compensates for the pumping insufficiency by dilating the ventricular chambers, thickening the walls (hypertrophy), and accelerating the pulsation rates.
More than 11 million patients currently suffer from CHF worldwide with a annual increase of about 10% of cases. Approximately 1 million patients present severe CHF conditions, and 1% are admitted in terminal condition. Nowadays, CHF is considered as the fastest-growing clinical cardiac disease entity in the United States, affecting 2% of the population. Nearly 1 million hospital admissions for acute decompensated CHF occur in the United States yearly, almost double the number seen 15 years ago. The rehospitalization rates during the 6 months following discharge are as high as 50%. Nearly 2% of all hospital admissions in the United States are for decompensated CHF, and heart failure is the most frequent cause of hospitalization in patients older than 65 years. The average duration of hospitalization is about 6 days. An estimated $23 billion are spent on inpatient management of CHF every year, and another $40 billion are spent in the outpatient setting on patients with compensated or mildly decompensated heart failure every year. Despite aggressive therapies, hospital admissions for CHF continue to increase, reflecting the prevalence of this malady.
Heart transplants have been the gold standard of treatment for end-stage CHF. A heart transplant is the replacement of a diseased heart with a healthy one from an organ donor. Candidates for transplant have irreparably damaged hearts, are facing imminent death, and have otherwise viable vital organs. Transplanted hearts generally fail 9.5 years (on average) after implantation. The American National Heart, Lung, and Blood Institute estimated that as many as 100,000 Americans would benefit from a transplant each year. Of these, fewer than 8,000 are ever placed on the national transplant waiting list, and only 2,000 to 2,500 hearts become available for transplantation. Most patients spend months or years waiting for a suitable donor heart and die before one becomes available. As of December 2006, 40,363 heart transplants have been performed in the United States. Nearly 85% of transplant recipients survive over one year following the procedure, and 70% survive for over 5 years. Over 3,000 transplants are performed worldwide each year, including 2,125 in the U.S. in 2005.
A ventricular assist device (VAD), is an electro-mechanical device that is used to partially or completely replace the function of a failing heart. Some VADs are intended for short term use, typically for patients recovering from heart attacks or heart surgery, while others are intended for long term use (months to years and in some cases for life), typically for patients suffering from CHF. VADs need to be clearly distinguished from artificial hearts, which are designed to completely take over cardiac function and generally require the removal of the patient's heart. VADs are designed to assist either the right (RVAD) or left (LVAD) ventricle. The choice of device depends on the underlying heart disease and the pulmonary arterial resistance which determines the load on the right ventricle. LVADs are most commonly used but when pulmonary arterial resistance is high, right ventricular assist becomes necessary. Long term VADs are normally used to keep patients alive with a good quality of life while they wait for a heart transplant.
Most VADs operate on similar principles. A cannula is inserted into the apex of the appropriate ventricle. Blood passes through this to a pump and thence through a tube to the aorta in the case of an LVAD or to the pulmonary artery in the case of an RVAD. The pump is powered through a lead which connects it to a controller and power supply. The first generation VADs, like the one described in U.S. Pat. No. 4,906,229, emulate the heart by using a pulsatile action where blood is alternately sucked into the pump from the left ventricle then forced out into the aorta. These devices are usually cumbersome and necessitate major surgery for their implantation into the vascular system and for introducing the cannula into the heart ventricule. More recent devices are based on intravascular continuous flow pumps, which can be roughly categorized as either centrifugal pumps, like in US 2004/0143151, or axial flow impeller driven pumps, like in U.S. Pat. No. 4,957,504. These second generation VADs have impellers with high flow rate capability and are much smaller than the first generation VADs, but have contacting bearings that suspend the rigid motor. The bearing contacts generally cause undesirable clot formation either inside or around the periphery of the bearings, making these devices unsuitable for long-term use. In these pumps, blood experiences traumatisation and damage due to shearing and vortexing into the small gaps between the outer edge of the stator blades and the inner side of the pipe carrying blood. Latest generation VADs overcome these issues by suspending the impeller in the pump using either hydrodynamic or electromagnetic suspension. therefore decreasing risks of thrombosis or hemolysis. Such pumps are described for example in U.S. Pat. No. 6,527,699 or US 2004/0115038.
The blood can be conveyed to the pump by an external tubular system, like in U.S. Pat. No. 6,742,999, and accelerated therein, but most of the blood pumps are implanted directly into the vascular system. Implantation of a blood pump inside the vascular system is disclosed for example in U.S. Pat. No. 7,144,364. A blood pump is attached to the interior of a stent and inserted into a peripheral artery by catheterisation and advanced to a position at a region of interest. The stent and attached pump are released from the catheter and the pump is activated to increase blood flow. However, implantability of current blood pumps is limited by their inherent characteristics. Latest generation blood pump are implanted in large vessels, as the whole device that comprises both rotor and stator, unavoidably occupies a large volume in the circulatory system. Furthermore, blood pumps have to be wired to a power supply and a controlling unit in order to generate a homogenous rotating electromagnetic field that activates the stator. Therefore perforation of the vascular system near the implantation site is required to allow passage of the wires.
It is an object to this invention to provide a permanent ventricular assist device (PVAD) that can allow a patient suffering from congestive heart failure to live a normal life.
It is further an object to this invention to provide a PVAD which overcome the disadvantages of prior art devices.
It is still another object to the present invention to provide a method to implant the PVAD of the invention in a region of interest.
Other objects and advantages of present invention will appear as description proceeds.